The present invention relates to optical disk recording devices for write-once optical disks such as CD-R (Compact Disk-Recorder) and CD-RW (Compact Disk Write-Once) media, and more particularly to wobble-signal reproduction circuitry employed in such optical disk recording devices.
Conventionally, in the pit-forming tracks of write-once optical disks such as CD-Rs and CD-RWs, there are formed grooves called xe2x80x9cpregroovesxe2x80x9d, which have pre-recorded therein absolute time information also known as ATIP (Absolute Time In Pregroove). Specifically, the ATIP information is recorded by wobbling the track grooves, and recording/reproduction control is performed on the basis of the ATIP information that is provided by reproducing signals representative of the track wobbles (hereinafter xe2x80x9cwobble signalsxe2x80x9d).
More specifically, the wobble signals of the optical disk are produced by processing outputs from a position-detecting photodetector of an optical pickup. Specifically, the position-detecting photodetector comprises, for example, a four-quadrant or four-part photodiode which is so named because it has a set of four light receiving surfaces A, B, C and D. Two combinations of the surfaces (A+D) and (B+C) form two composite light receiving surfaces that are divided in the radial direction of the optical disk along a demarcation line extending along the tracks, and other two combinations of the surfaces (A+B) and (C+D) form other two composite light receiving surfaces that are divided in the radial direction of the optical disk along another demarcation line extending in a direction transverse to the tracks. EFM (Eight to Fourteen Modulation) signals modulated on the basis of presence/absence of pits in the optical disk are each detected in the same phase by the light receiving surfaces A, B, C and D, while the wobble signals are each detected in opposite phases by the two composite light receiving surfaces (A+D) and (B+C). The wobble signal can thus be extracted by performing a subtraction between light detection signal outputs from the two-composite light receiving surfaces (A+D) and (B+C) to thereby remove the EFM signal components therefrom.
Conventional wobble-signal reproduction circuitry is constructed typically in a manner as shown in FIG. 9. Namely, sample-and-hold (S/H) circuits are provided in corresponding relation to the outputs from the light receiving surfaces of the four-quadrant photodiode. The outputs from the first combination of the light receiving surfaces are added together, and similarly the outputs from the second combination of the light receiving surfaces are added together, so as to provide signals indicative of the added results (A+D) and (B+C) (i.e., (A+D) signal and (B+C) signal). Then, a wobble signal is produced by performing a subtraction between the added results (A+D) and (B+C). In recording, a sampling operation is carried out to sample the light detection signals (i.e., return light, from the optical disk, of laser light modulated by the EFM signal) output from the sample-and-hold (S/H) circuits by capturing their respective bottom power levels, as illustrated in FIG. 10. However, in reproduction, the sample-and-hold (S/H) circuits are all maintained in a xe2x80x9cthroughxe2x80x9d, i.e., xe2x80x9cnon-sampling/holdingxe2x80x9d state.
Because the high-frequency EFM signal components contained in the (A+D) and (B+C) signals are in the same phase, the EFM signal components can be cancelled out, in the reproduction process, by performing a subtraction between the (A+D) and (B+C) signals as long as these signals are equal in level, so that the conventional wobble-signal reproduction technique can provide a wobble signal with no adverse influence. If, however, there is a level difference between the (A+D) and (B+C) signals, the undesired EFM signal components cannot be completely removed from the wobble signal, which would lead to the inconvenience that accurate ATIP information cannot be obtained through the conventional wobble-signal reproduction technique.
To provide a solution to the above-mentioned inconvenience, a novel technique has been proposed, e.g., in Japanese Patent Application Laid-Open Publication Nos. HEI-6-44568 and HEI-8-63766, which is intended to improve the quality of the wobble signal by adjusting the amplitude levels of the EFM signal components, in the (A+D) and (B+C) signals, to equal each other. However, the proposed technique would require extra circuits, such as a variable gain circuit, to make the amplitude levels of the EFM signal components equal to each other.
Further, in the recording process, performing the sample-and-hold operation would entail problems, such as production of undesired noise at the rise and fall time of sampling pulses and holding offsets. Particularly, in the case of high-speed recording, a C/N (Carrier-to-Noise) ratio and quality of the wobble signals would greatly deteriorate because the sampling pulse widths are significantly narrowed. FIG. 11 shows a typical relationship between the light detection signal (representative of detected return light from the optical disk) and the sampling pulses, on a greater scale than FIG. 10. As seen from FIG. 11, a time difference xcfx84 between fall timing of each pulse of a recording signal and rise timing of each sampling pulse is constant irrespective of a recording speed, so that the duty cycle of the sampling pulses decreases as the recording speed is increased, which would create deterioration of the C/N ratio.
It is therefore an object of the present invention to provide an optical disk recording device equipped with wobble-signal reproduction circuitry which, with a simple structure, permits production of a high-quality wobble signal free of high-frequency signal component leaked thereto.
According to a first aspect of the present invention, there is provided an optical disk recording device for recording data onto a write-once optical disk having a track wobbled on the basis of absolute time information, the optical disk recording device comprising: a beam projection section for projecting a light beam onto the optical disk; a photodetector having at least two light receiving surfaces divided in a radial direction of the optical disk for detecting reflected light from the optical disk; and wobble-signal reproduction circuitry for reproducing a wobble signal corresponding to a wobble of the track on the basis of first and second light detection signals output from the two light receiving surfaces of the photodetector, and which is characterized in that the wobble-signal reproduction circuitry includes: first and second peak-holding circuits for, when the optical disk recording device is in a reproduction mode, detecting and holding respective upper envelopes of the first and second light detection signals output from the photodetector; first and second bottom-holding circuits for, when the optical disk recording device is in a recording mode, detecting respective lower envelopes of the first and second light detection signals output from the photodetector; and a subtraction circuit for producing a wobble signal by performing a subtraction between values held by the first and second peak-holding circuits when the optical disk recording device is in the reproduction mode and performing a subtraction between values held by the first and second bottom-holding circuits when the optical disk recording device is in the recording mode.
According to a second aspect of the present invention, there is provided an optical disk recording device for recording data onto a write-once optical disk having a track wobbled on the basis of absolute time information, the optical disc recording device comprising: a beam projection section for projecting a light beam onto the optical disk; a photodetector having at least two light receiving surfaces divided in a radial direction of the optical disk for detecting reflected light from the optical disk; and wobble-signal reproduction circuitry for reproducing a wobble signal corresponding to a wobble of the track on the basis of first and second light detection signals output from the two light receiving surfaces of the photodetector, and which is characterized in that the wobble-signal reproduction circuitry includes: first and second polarity switching circuits for inverting polarities of the first and second light detection signals output from the photodetector, depending on whether the optical disk is in a reproduction mode or in a recording mode; first and second holding circuits for, when the optical disk recording device is in the reproduction mode, detecting and holding respective upper envelopes of the first and second light detection signals passed from the first and second polarity switching circuits and, when the optical disk recording device is in the recording mode, detecting and holding respective lower envelopes of the first and second light detection signals passed from the first and second polarity switching circuits; and a subtraction circuit for producing a wobble signal by performing a subtraction between values held by the first and second holding circuits.
By holding the bottom or peak values of the two light detection signals, for reproduction of the wobble signal, depending on whether the optical disk recording device is in the reproduction mode or in the recording mode, the present invention can remove high-frequency signal components of the EFM signal. Thus, the present invention can effectively prevent leakage of the high-frequency signal components into the reproduced wobble signal, without a need to adjust the EFM signal level using a separate level-adjustment circuit. Further, because no sample-and-hold circuit is employed in the present invention, it is possible to avoid the problematic C/N ratio deterioration that heretofore occurred in cases where the sample-and-hold circuit is used.